Aeroponics, or the growth of plants in air has been known for some time. F. W. Went describes experimental apparatus for growing plant roots in a vaporized nutrient in a publication entitled "The Experimental Control of Plant Growth" (1957) Chronica Botanica Co. Waltham, Mass. at pages 81-83. Even earlier, in a publication entitled "A Method of Growing Plants in Water Vapor to Facilitate Examination of Roots", Phytopathology Volume 32 pages 623-625, 1942, W. A. Carter described apparatus for growing plants with their roots in water vapor. More recently, in an article entitled "Method for Growing Plants Aeroponically", in Plant Physiology (1976) Vol. 57, pages 344-346, Zobel et al describe an experimental growing box employing a rotating spinner for mist generation.
The above publications, extending over more than 30 years, all relate to experimental devices designed to permit examination and relatively free access to plant roots for treatment, all within a research context. Aeroponics, until the present, has been confined to the laboratory and has not been conceived of or developed heretofore as a commercial technique for facilitating and enhancing plant growth and development.
A number of cogent reasons why plants should be grown commercially outside of a soil environment have long existed. A major problem particularly in the growth of flowers are diseases which reach the plant via the soil. For example, bacteria such as Fussarium, present in certain soils, causes disease in Carnation plants. Other examples of plant diseases which arise from soil contact are Botrytis, Sclerotium, Verticilium and Rhizoctonia. Further difficulties connected with soil borne diseases are the difficulty of diagnosing and treating the plants and particularly the root portions thereof due to the relative inaccessibility thereof in the soil.
Other difficulties arise in connection with plants which require special and specific treatment to enhance their growth.
For example, in the case of orchids, it has been found desirable to supply certain hormones to the growing plants in order to enhance their development. The application of such hormones to such plants in a soil environment is rendered difficult and relatively expensive due to the relatively large quantity of material required, arising from the fact that such hormones must be administered indirectly, via the soil.
Hydroponics, or the growth of plants in water, has been known for some time and has been the subject of much experimental investigation. Hydroponics has not however achieved acceptance for commercial scale plant growth and development. One problem often involved in hydroponics is the lack of adequate ventilation at the roots due to the substantially continuous presence of water thereabout.
Hydroponic plant growth apparatus employing a liquid spray has been proposed in the patent literature. U.S. Pat. No. 4,059,922 discloses a sprayer hydroponic grower in which potted plants are mounted on a supporting frame defining a spray enclosure. The pots are apertured to permit the spray to wet the root portions of the plants and to provide nutrients thereto. The roots of the plants are supported within the pots by a porous medium such as peat and thus the majority of the roots are not directly exposed to the atmosphere and to the spray. As a result of the retention of moisture by the porous medium, spray is provided only two or three times during a 24 hour period. The fact that the roots are in the main not directly exposed to the atmosphere is believed to have negative implications with regard to root diseases.
U.S. Pat. No. 2,431,890 discloses a method and receptacle for propagating plants and relates particularly to cuttings to which a spray of water is applied to facilitate the development of roots.
U.S. Pat. No. 3,768,201 discloses a method of sprouting beans which employs a water spray which is governed by a timer. The beans to be sprouted are disposed in a container having an apertured bottom for draining and the water is recirculated.
German Offenlegungsschrift No. 2,351,508 describes a plant growing method in which plants are matured from seed which is placed in a porous root permeable base. As the plant develops, the roots extend outwardly of the root permeable base. The base is mounted on a support frame such that the base and the exterior roots are exposed to a liquid spray. The porous root permeable base shares the apparent disadvantages of the pots of U.S. Pat. No. 4,059,922, in that a portion of the roots is not exposed to the atmosphere and to the spray and thus becomes susceptible to root disease.